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Mon, 10 Feb 2025 18:44:21 GMT Received: from smtpav03.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C2B9120043; Mon, 10 Feb 2025 18:44:21 +0000 (GMT) Received: from smtpav03.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BED5620040; Mon, 10 Feb 2025 18:44:19 +0000 (GMT) Received: from li-7bb28a4c-2dab-11b2-a85c-887b5c60d769.ibm.com.com (unknown [9.39.21.225]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 10 Feb 2025 18:44:19 +0000 (GMT) From: Shrikanth Hegde To: maddy@linux.ibm.com, linuxppc-dev@lists.ozlabs.org, christophe.leroy@csgroup.eu Cc: sshegde@linux.ibm.com, mpe@ellerman.id.au, npiggin@gmail.com, bigeasy@linutronix.de, will@kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v4 1/1] powerpc: enable dynamic preemption Date: Tue, 11 Feb 2025 00:13:34 +0530 Message-ID: <20250210184334.567383-2-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.43.5 In-Reply-To: <20250210184334.567383-1-sshegde@linux.ibm.com> References: <20250210184334.567383-1-sshegde@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 X-Proofpoint-GUID: iIMnPBp5X1NCCjhrT4KnZ8dHCfELt2_W X-Proofpoint-ORIG-GUID: rnMB2gwvS1vmqrKMDNXHmGBtR3DlZvi6 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-02-10_10,2025-02-10_01,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 phishscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 malwarescore=0 mlxscore=0 suspectscore=0 clxscore=1015 lowpriorityscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2501170000 definitions=main-2502100149 Content-Type: text/plain; charset="utf-8" Once the lazy preemption is supported, it would be desirable to change the preemption models at runtime. So add support for dynamic preemption using DYNAMIC_KEY. ::Tested lightly on Power10 LPAR Performance numbers indicate that, preempt=3Dnone(no dynamic) and preempt=3Dnone(dynamic) are close. cat /sys/kernel/debug/sched/preempt (none) voluntary full lazy perf stat -e probe:__cond_resched -a sleep 1 Performance counter stats for 'system wide': 1,253 probe:__cond_resched echo full > /sys/kernel/debug/sched/preempt cat /sys/kernel/debug/sched/preempt none voluntary (full) lazy perf stat -e probe:__cond_resched -a sleep 1 Performance counter stats for 'system wide': 0 probe:__cond_resched Signed-off-by: Shrikanth Hegde --- arch/powerpc/Kconfig | 1 + arch/powerpc/include/asm/preempt.h | 16 ++++++++++++++++ arch/powerpc/kernel/interrupt.c | 6 +++++- arch/powerpc/lib/vmx-helper.c | 2 +- 4 files changed, 23 insertions(+), 2 deletions(-) create mode 100644 arch/powerpc/include/asm/preempt.h diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index 424f188e62d9..364edaea1f88 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -275,6 +275,7 @@ config PPC select HAVE_PERF_EVENTS_NMI if PPC64 select HAVE_PERF_REGS select HAVE_PERF_USER_STACK_DUMP + select HAVE_PREEMPT_DYNAMIC_KEY select HAVE_RETHOOK if KPROBES select HAVE_REGS_AND_STACK_ACCESS_API select HAVE_RELIABLE_STACKTRACE diff --git a/arch/powerpc/include/asm/preempt.h b/arch/powerpc/include/asm/= preempt.h new file mode 100644 index 000000000000..000e2b9681f3 --- /dev/null +++ b/arch/powerpc/include/asm/preempt.h @@ -0,0 +1,16 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __ASM_POWERPC_PREEMPT_H +#define __ASM_POWERPC_PREEMPT_H + +#include + +#if defined(CONFIG_PREEMPT_DYNAMIC) +#include +DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched); +#define need_irq_preemption() \ + (static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched)) +#else +#define need_irq_preemption() (IS_ENABLED(CONFIG_PREEMPTION)) +#endif + +#endif /* __ASM_POWERPC_PREEMPT_H */ diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrup= t.c index 8f4acc55407b..e0c681d0b076 100644 --- a/arch/powerpc/kernel/interrupt.c +++ b/arch/powerpc/kernel/interrupt.c @@ -25,6 +25,10 @@ unsigned long global_dbcr0[NR_CPUS]; #endif =20 +#if defined(CONFIG_PREEMPT_DYNAMIC) +DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched); +#endif + #ifdef CONFIG_PPC_BOOK3S_64 DEFINE_STATIC_KEY_FALSE(interrupt_exit_not_reentrant); static inline bool exit_must_hard_disable(void) @@ -396,7 +400,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(str= uct pt_regs *regs) /* Returning to a kernel context with local irqs enabled. */ WARN_ON_ONCE(!(regs->msr & MSR_EE)); again: - if (IS_ENABLED(CONFIG_PREEMPTION)) { + if (need_irq_preemption()) { /* Return to preemptible kernel context */ if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) { if (preempt_count() =3D=3D 0) diff --git a/arch/powerpc/lib/vmx-helper.c b/arch/powerpc/lib/vmx-helper.c index 58ed6bd613a6..54340912398f 100644 --- a/arch/powerpc/lib/vmx-helper.c +++ b/arch/powerpc/lib/vmx-helper.c @@ -45,7 +45,7 @@ int exit_vmx_usercopy(void) * set and we are preemptible. The hack here is to schedule a * decrementer to fire here and reschedule for us if necessary. */ - if (IS_ENABLED(CONFIG_PREEMPTION) && need_resched()) + if (need_irq_preemption() && need_resched()) set_dec(1); return 0; } --=20 2.39.3